Metal nitrates are useful metal oxide precursors due to their relatively low cost and ease of manufacture. They are often converted into the corresponding metal oxides in catalyst or sorbent manufacture. In catalyst or sorbent manufacture typically one or more soluble metal nitrates is impregnated onto a suitable support material, and dried to remove the solvent. The impregnated support is then usually heated under air, in a step often called calcination, to an elevated temperature at or above the decomposition temperature of the metal nitrate to form the metal oxide. However, such a method does not always lead to satisfactory oxidic materials. In particular, where the metal oxide is a reducible metal oxide, the dispersion and distribution of crystallites of the metal oxide and hence reduced metal obtained by these processes is often poor.
Variations on this preparative method have been attempted. EP0421502 describes a process for the preparation of a catalyst or catalyst precursor wherein cobalt nitrate supported on a porous inert carrier is calcined in an atmosphere containing at least 20% volume nitrogen oxide (not taking the water content of the atmosphere into consideration). The nitrogen oxides preferably originated from the decomposition of cobalt nitrate under conditions where the calcination oven was not purged or purged at low velocity. Such calcination was stated to produce agglomerates of cobalt oxide crystallites with dimensions in the range 1 to 10 micrometers.
In the aforesaid EP0421502 calcination of the cobalt nitrate was performed in air, with the nitrogen oxide being provided by the metal nitrate itself. Whereas the specific nitrogen oxide was not stated, the nitrogen oxide predominant during such calcination will be nitrogen dioxide (NO2).
Supported metal oxides find use as catalysts, catalyst precursors and sorbents whose effectiveness is related to the dispersion of the metal oxide on the support. Therefore there is a desire to improve the dispersion of metal oxides derived from metal nitrates.